Also: I'm confused by what you mean when you say "core" classes. - Edit 1
Before modification by lord-of-shadow at 18/06/2010 04:31:13 AM
By definition (the definition I use, at least!), the classes in the Player's Handbook 1 ARE the core classes. All others, from any other source, are extra. The core game consists of the content and rules from the core 3 books - Player's Handbook, Dungeon Master Guide, and Monster Manual - and everything else afterwards is additional content.